EXAMPLES ON CHAPTERS 6
--------------------------------------------1-Given the following notation for an electrochemical cell
Pt(s) | H2(g) | H+(aq) | | Ag+(aq) | Ag(s )
what is the balanced overall (net) cell reaction
a) H+(aq) + 2Ag+(aq) → H2(g) + 2Ag(s)
b) H2(g) + 2Ag+(aq) → 2H+(aq) + 2Ag(s)*
c) H2(g) + Ag+(aq) → H+(aq) + Ag(s)
d) 2H+(aq) + 2Ag(s) → H2(g) + 2Ag+(aq)
2- A certain electrochemical cell has for its cell reaction
Zn + HgO → ZnO + Hg
Which is the half-reaction occurring at the anode?
a) HgO + 2e– → Hg + O2–
b) Zn2+ + 2e– → Zn
2+
c) Zn → Zn + 2e *
d) ZnO + 2e– → Zn
3- Calculate the value of E°cell for the following reaction
2Au(s) + 3Ca2+(aq) → 2Au3+ (aq) + 3Ca(s)
0
If E Au3+/Au = 1.5V and E0Ca2+= -2.9V
a) -4.37 V*
b)-1.37V
c) + 4.37
d) – 11.6
4- Which statement is true in regard to a spontaneous redox reaction?
a) E°red is always negative
b) E°cell is always positive*
c)E°ox is always positive
d) E°red is always positive
5- Determine the equilibrium constant, Keq, for the reaction
2Br-(aq) + I 2(s)
a) 5.3 10
–19 *
b)18.30
Br2(l) + 2I-(aq)
c) 1.9x1018
d) 18.3x10-19
6-Calculate the cell emf for the following reaction
Ni(s) + 2Cu+ (0.010 M) → Ni2+ (0.0010 M) + 2Cu(s)
0
If E Ni++/Ni = - 0.25
E0 Cu+/Cu = +0.521
a) 0.40 V
b) -0.43 V
c) 0.37 V*
d) 0.37 V
7-The half-reaction that occurs at the cathode during electrolysis of aqueous CuCl2 solution is
a) Cu+ + e– → Cu
b) Cu2+ + e– → Cu* c) 2Cl– → Cl2 + 2e–
d) 2H2O + 2e– → H2 + 2OH8-A metal object is to be gold-plated by an electrolytic procedure using aqueous AuCl3 electrolyte.
Calculate the number of moles of gold deposited in 3.0 min by a constant current of 10 A
a) 6.2 x10-3 mol *
b) 9 x10-3 mol
c) 1.8 x10-2 mol
d) 160 mol
9- How many grams of nickel would be electroplated by passing a constant current of 7.2 A through a
solution of NiSO4 for 90.0 min?
a) 0.20 g
b) 0.40 g
c)12g *
d) 24g
10-How many minutes would be required to electroplate 25.0 grams of chromium by passing a constant
current of 4.8 amperes through a solution containing CrCl3?
a)483 min. *
b) 161min.
c)322min.
d)1112min.